Information of a profile and a size of a defect may be quickly and effectively obtained by using an ultrasonic Lamb wave tomography. A Lamb wave time-of-flight cross-hole tomography may perform a fan-beam projection and imaging by means of a linear transducer array, which is an iteration-based effective and quick tomography. The traditional Lamb wave time-of-flight cross-hole tomography is based on a straight ray theory, i.e., assuming that the Lamb wave travels in straight lines after encountering a defect in a propagation process. However, the propagation direction of the Lamb wave is deflected if a plate has a strong scattering defect. That is, the Lamb wave travels in curve. At this time, the straight ray theory is inapplicable, and the precision of the tomography is decreased. The above problem is a bottleneck confining the development of the Lamb wave time-of-flight cross-hole tomography.